Carbon paper and method of making same



Feb. 25, 1958 M. L. DOWNS ETAL 2,824,815

CARBON PAPER AND METHOD oF MAKING SAME Filed Jan. 18, 1956 PHP5? CHROM/0M CARBON PAPER AND ME'I'HD F MAKING SAME Martin L. Downs and Robert C. Dressler, Appleton, Wis.,

assignors to Thiimany Pulp & Paper Company, Kaukauna, Wis., a corporation of Wisconsin Application .lanuary 1S, 1956, Serial No. 559,799

3 Claims. (Cl. 117-36) The present invention relates generally to improvements in the manufacture of carbon paper, and more particularly, it relates to the provision of carbon paper having improved write-olf characteristics, limited streaking and pinholing, and greater facility for manufacture.

Carbon paper is a particular paper in the paper converting industry which has certain well known characteristics. As is known, carbon paper is used for making duplicate or carbon copies with' a pen, pencil or typewriter, and consequently, it comprises a thin tissue sheet usually having a basis weight ranging from about 4 pounds to about l5 pounds per ream of 500 sheets which are inches by 30 inches. The sheets are usually coated on one side, but they may be coated on both sides.

The coating usually comprises coloring matter, such as a pigment or dye, which is carried in a vehicle. The vehicle generally comprises a thermoplastic material. The mixture of coloring matter and vehicle, that is, the colored vehicle, is applied by a coating machine including rolls which pick up the mixture and apply it to the thin sheets. The vehicle itself is in molten from at the time of application.

Because of the light weight, and consequent thinness of the sheets, the sheets have small openings or pinholes. When the colored vehicle is applied to the sheets, it has a tendency to penetrate the pinholes and frequently will offset on the reverse side when going through the coating equipment, causing spotting and streaking. The formation of these spots and streaks is referred to herein as pinholing, spotting and streaking.

The difficulty of pinholing, spotting or streaking is partially eliminated by means of several steps, all of which are time consuming and expensive. Thus, the paper can be made either heavier or denser and shorter bered. But both these steps increase the cost of the base paper. Moreover, it is desirable to keep the paper long fibered and porous so as to maintain strong tearing resistance and other properties.

rl`he application of various materials to the face of the paper has been only partly effective in reducing pinholing, spotting or streaking. In addition, such treatments have materially reduced the strength of the paper and introduced stilfness.

The use of additional paper weight is also objectionable for reasons outlined above, and the use of denser papers, in addition to increasing their production cost, results in a sheet which is mechanically weaker.

Pinholing and streaking can also be reduced by utilizing lower coating temperatures so that the coating is more viscous and plastic, and by lowering the speed of the coating equipment. Furthermore, the coating pressure may be reduced to limit pinholing and streaking. However, each of these expedients results in increased production costs through the use of increased amounts of the coating material or loss in production.

Accordingly, the main object of this invention is the provision of an improved carbon paper, and particularly, a carbon paper which does not have objectionable spots,

streaks, smudges or smears on the uncoated side, while at the same time permitting rapid and economical manufacture of the carbon paper.- Other objects of the present invention will be apparent from a study of the following detailed description and of the accompanying drawing, in which:

Figure l is a flow diagram of a preferred embodiment of the process of the present invention; and,

Figure 2 is an enlarged, fragmentary sectional view of carbon paper of the present invention, prepared in accordance with the process set forth in Figure 1.

ln accordance with the present invention, an oleophobic and hydrophobic, non-film forming substance is applied to a light weight sheet, thereby maintaining the porosity of the sheet and minimizing pinholing and streaking. Thus, through the utilization of this invention, higher coating temperatures and higher coating speeds with greater applicating pressures can be utilized in the manufacture of carbon paper.

In the practice of our invention, we apply an oleophobic and hydrophobic substance which is non-film forming to a sheet having a basis weight of below about l5 pounds per ream (500 sheets-20" x 30"). The amount of such substance should be such that the porosity of the sheet is substantially unimpaired but should not be so low as to permit pinholing streaking. While the operating conditions used with the coating equipment, such as temperature of the thermoplastic coating mixture, the speed of coating and the pressure eX- erted during coating, in part control the amount of the oleophobic, hydrophobic material required, we havev found that the amount of such material should be greater than about .02 percent and less than about .5 percent of the weight of the sheet.

As a test procedure, we apply a molten paraiiin wax (melting point 138 F.) containing an oil soluble dye, at a temperature of F. to a sheet to a depth of onequarter (1/4) inch. The wax is allowed to cool and the opposite or uncoated side of the sheet is examined. The amount of treatment of the sheet should be such that there is no substantial penetration of the sheet or ow through the pinholes.

As has been pointed out, the material which is applied l to the sheets should be a non-film forming, oleophobic and hydrophobic material. In this connection, we have found that a highly desirable material of this type is a metal complex of a fluorinated organic acid, and particularly, we have found that chromium coordination complexes of saturated peruoromonocarboxylic acids are highly satisfactory. In order to provide the desired properties, the latter acids should have more than four and less than ten carbon atoms in the acid molecule. The chromium coordination complexes of saturated periiuoromonocarboxylic acids are well known and are commercially available. In this connection, such compounds are prepared and are distributed by the Minnesota Mining and Manufacturing Company under the name of ScotchGard, No. FC-804. As has been pointed out, the material should be added to the thin sheets in amounts between about .O2 and about .5 percent.

The material, in its intermediate stage, i. e., prior to heat treament or aging, is, when concentrated, soluble only in alcohol but becomes soluble in water upon large dilution, the sheet becomes hydrophobic and oleophobic in character. Accordingly, the material is preferably dissolved in a solvent but it may be emulsiiied. The thin sheets may then be passed through the liquidV containing the hydrophobic, oleophobic material in its intermediate or emulsiied state. The liquid, of course, may be sprayed onto the thin sheets.

After the liquid is applied to the thin sheets, the sheets and uponheat treatment after being applied to as doctoring VVfer rolls, squeeze rolls or like equipment.

are dried and heated heating being done undeisuch conditions as to convert the material in the liquid to the ol'eophobicVV and hydrophobic state. After Vsuch drying andV heating, Vthe colored vehicle is applied to'the sheet.

The vehiclemaypcomprise blends of one or more syn- Vthetic orV natural waxes such as parain, carnauba,Y Y Frequently, fatty orV wax 1' alcohols are added inv order to solubilize the dyes.` The candelilla, and other waxes.

Vvehicle maybe colored with carbon black, nigrosine oil f soluble base, methyl Violet oil soluble base, various inks,

' the colored'vehicleonto the sheet.

stantial hydrostatic pressure was developed and the coated vehicle was Y'applied at the rate of 3.1 pounds of coating per ream of paper. This sheet exhibited improved write-V Y, ott characteristics when compared to a control sample,

and other wellknown coloring materials. it is common Y practice to combine the vehicle with ther'coloring ma-V terial in a ball mill at temperatures above the melting point of theconstituent materials.

Following preparation of the colored vehicle, itis applied to the treated thin sheets at temperatures Vabove the melting point of the colored vehicle, usually at tern- Y peratures in the range between about 170 F. and aboutv 240 F. The Vcolored vehicle or coating may be applied V in excess-and adjusted to the proper amount onV the sheets by `means of blades or rods, referred to generally Alternatively, the coating maybe applied in metered or controlled arnounts'by multiple transmethod of application, the coating material is applied to Vthethin sheetswhile the material is hot and in a 1 carbon paperand an impression is then formed by typing orV writing onV the top sheet, the series of impressions I formed'fon the subsequent sheets will be improved. Secondly, the product V.of the invention may be made with reduced amounts of `coating material,Y while providing v equivalent results in duplication, if e., write-olf. `Furthermore, the practice Vofthe invention permits faster coating of the. thinsheets while, at the same time, reducing Y pinholing, spotting and streaking. Y

in Van actual commercial operation, carbon paper vhav- Y ing a basislweight of l() poundsper ream (20 inches byV In either 30 inches for 500 sheets) was employed. The sheet was Vmade from a kraft pulp furnish. A solution ot' chromium coordinated complex of saturated perfluoromonocarboxylic acid wasprepared. The complex was YScotchV Gard No. FC-804. The paper Was passed through the solution, the pickup ofthe chemical ranging from 0.1 to 0.25 percent ofthe weight of the sheet, and was then dried` to 5 percent moisture bypassing through a steam heated paper machine dryer. Y Y The sheet was .then run through a conventionalfcar- Yboniring machineand, in one case, an excess of colored vehicle was applied and theV` amount of material adjusted Y by means` of Y.an equalizer rod. The vehicle Vwas of a.

blue color and was coated onto the sheet at a temperature of 200 F. T he coating weighed 2.93 pounds .per ream.

The use of theequaiizer rod -develops a ysubstantial amount of hydrostatic pressure uponV the sheet at the nip between the paper surface and the equalizer Vrod so thatthe coating may be .squirted through any. pores or pinholes in the'sheet. jectionable spotting, streaking or pinholing on the unf coated side of the treatedV sheet, although a control sample which was run through the machine had quite ob- However, there wasno ob-y l cule, the amount of Asaidchromium coordination com-V plex'being between about .02 and about .Srpe'rcent ofV .Y the weight of said base sheet, and a. pigmented wax coat-pV jectionable spotting, streaking and pinholing. The sheet Y which has been treated in accordance with this invention has improved write-oil characteristics.

11n another run, the colored vehicle was applied to the sheet by means Yof transferrollsiwhich, in effect, lprinted In this run, no subthe base sheet of which had not been `,treated in,v accordance with our invention.

ln a laboratoryV test, we employed a base sheet having a weight of l0 `pounds (20 inchesfby V30 inches for 500 sheets) and Ytreated this. paper l to provide aV level of Vchromium coordinated .complex'of saturated periluoromonocarboxylic acidV betweenl percent and .25 Vpercent. To Vthe treated sheet was applied molten parain waxcontaining an oil soluble dyethe waxbeing at a temperatureof F. K The waxwas applied and maintained at a level on the sheet ofv one-quarter (A) 'of an inch. The Waxwas allowed'torcool. VUpon examinar--V tion of the sheet, it was apparent that in all ca's'es'gthe' penetration of the wax was. substantially reduced; as

compared to a control sheet to whichno chemicalwas' applied. in the case of eachof the treatedsheets, there was no marking of a'backing paperY but, in the vvcase Vofi the control, the backing paper Vwas marked with y.

From theV foregoing, it willbe quite apparentthat in'`Y Y the practice of the invention, highly VimprovedV carbonpaper is provided and production of such paper is greatly Y facilitated. Y Y p Various features of the invention vwhich arebelieved to be new are set forthV in the following claims..

We claim:V Y

l, An improved process for the manufacture of carbon paper comprising the stepsV of applying a .non-lm forming chromium coordination complex` ofsaturated peruoromonocarhoxylic acid, the acid molecule havingV more than l4 and less than lOcarbon atoms inthe mole-.1,

cule, to a sheet having a basis weight ofbetweenabout 4 pounds and aboutV l5 poundsperream (20 inches'by`30 inchespfor 500 sheets), said material being applied tofsaidv sheet in anamount of between about .02 and .5 percent of the weightof said sheet, and Ycoating saidsheet with VaV melted pigmented waxV vehicle. Y Y

2. A carbonV paper comprising a base sheet having a basis weight of between about :.4 pounds and aboutV 15 pounds per ream (Zl'inches by 30 inches for500`sheets),

said base sheet being impregnated. with a non-film. form.-

ing chromium coordination complex `of .a saturated perfv tluorernonocarboxylic acid, the acidV moleculeV having more than 4 and less than kl() carbon atoms'inthe molegY Y Y Y Y eule, the amount of said chromium coordination complex being between about .02 and about .5 percent of the Y weight of .said base sheet, and a thermoplastic coating on said base sheet, the carbon, paper being' substantially free fromspots'and streaks. i

3. A carbon paper ,comprising a baise sheet having a y. basis weight of between about 4 pounds ,and about l5 pounds per rearn (20 inches byj30 Vinches for 500 sheets),

said base sheet being impregnated withY a non-hlm form-V .i

ing chromium coordination complex of Ya saturated per.-

noromonocarboxylic acid, the acid i molecule having more than 4 and'less than Vl0 carbon atoms in the moleing on said base sheet, the carbonY paper beingl substantially free from spots and streaks.v Y Y References Cited inthe le'of thispateut UNITED STATES PATENTSr 1,925,235 Dam septf5, V193sV 2,606,775 n Newman Aug. 12, i952 2,662,835y VReid Dec.Y 15, 1953 2,693,458`

Olson i uo-v; 2; 1954 

1. AN IMPROVED PROCESS FOR THE MANUFACTURE OF CARBON PAPER COMPRISING THE STEPS OF APPLYING A NON-FILM FORMING CHROMIUM COORDINATION COMPLEX OF SATURATED PERFLUOROMONOCARBOXYLIC ACID, THE ACID MOLECULE HAVING MORE THAN 4 AND LESS THAN 10 CARBON ATOMS IN THE MOLECULE, TO A SHEET HAVING A BASIS WEIGHT OF BETWEEN ABOUT 4 POUNDS AND ABOUT 15 POUNDS PER REAM (20 INCHES BY 30 INCHES FOR 500 SHEETS), SAID MATERIAL BEING APPLIED TO SAID SHEET IN AN AMOUNT OF BETWEEN ABOUT .02 AND .5 PERCENT OF THE WEIGHT OF SAID SHEET, AND COATING SAID SHEET WITH A MELTED PIGMENTED WAX VEHICLE. 